Process for fabricating structurally robust optical coatings

Abstract

A novel molecular beam epitaxy deposition process for precisely growing structurally robust films and coatings containing germanium and various fluoride compounds for use as an optical filter. The process comprises depositing two (2) materials having different indices of refraction via molecular beam epitaxy at a temperature significantly lower than the optimal growth temperature. At such lower temperature, layers of the respective compounds are grown, via molecular beam epitaxy, such that the layers contain large concentrations of dislocations. Once the film or coating has been grown to the desired thickness, the material deposited is allowed to cool to room temperature and may then be used in a wide range of applications.

What is claimed is: 
     
       1. A process for forming a structurally robust optical coating upon a substrate comprising the steps of: (a) epitaxially growing first and second compounds upon said substrate such that a resultant coating is formed thereon, said first compound having a first index of refraction and said second compound having a second index of refraction, said first index of refraction being different from said second index of refraction; and   (b) promoting the formation of dislocations within said resultant coating such that the density of dislocations formed therein causes said coating to substantially withstand cracking when cooled from said temperature at which said first and second compounds are epitaxially grown upon said substrate.   
     
     
       2. The process of claim 1 wherein said first compound has a first index of refraction less than two (2) and said second compound has a second index of refraction greater than two (2). 
     
     
       3. The process of claim 1 wherein in step (a), said first and second compounds are grown by molecular beam epitaxy. 
     
     
       4. The process of claim 1 wherein said first compound comprises germanium and said second compound is selected from the group consisting of strontium fluoride, calcium fluoride and lithium fluoride. 
     
     
       5. The process of claim 1 wherein in step (b), said temperature is regulated to be lower than 600° C. 
     
     
       6. The process of claim 1 further comprising the step of: (d) regulating the thickness of said optical coating to be between 1 and 2 μm.   
     
     
       7. A process for depositing an optical coating upon a substrate comprising the steps of: (a) epitaxially growing first and second compounds upon said substrate such that a resultant coating is formed thereon, said first compound having a first thermal expansion co-efficient and said second compound having a second thermal expansion co-efficients, said first thermal expansion co-efficient being different from said second thermal expansion co-efficient; and   (b) promoting the formation of dislocations within said resultant coating such that the density of dislocations formed therein causes said coating to substantially withstand cracking when cooled from said temperature at which said first and second compounds are epitaxially grown upon said substrate.   
     
     
       8. The process of claim 7 wherein in step (a), said first and second compounds are grown by molecular beam epitaxy. 
     
     
       9. The process of claim 7 wherein said first compound comprises germanium and said second compound is selected from the group comprising strontium fluoride, calcium fluoride, or lithium fluoride. 
     
     
       10. The process of claim 7 further comprising the step of regulating the thickness of said optical coating to be between 1 and 2 μm. 
     
     
       11. A process for depositing an optical coating comprised of germanium and strontium fluoride upon a substrate comprising the steps: (a) epitaxially growing a layer of germanium and strontium fluoride upon said substrate; and   (b) regulating the temperature at which said layer of germanium and strontium fluoride is grown such that there is caused to form a multiplicity of dislocations within said layer such that the density of said locations formed therein prevents said layer of germanium and strontium fluoride to withstand cracking when cooled from said temperature which said layer of germanium and strontium fluoride are epitaxially grown.   
     
     
       12. The process of claim 7 wherein in step (b), said temperature is regulated to be approximately 400° C. 
     
     
       13. The process of claim 7 further comprising the step of regulating the thickness of said optical coating of germanium and strontium fluoride to be between 1 and 2 μm. 
     
     
       14. The process of claim 1 wherein in step (b) said step of promoting the formation of said dislocations within said resultant coating comprises regulating the temperature at which said first and second compounds are epitaxially grown. 
     
     
       15. The process of claim 7 wherein in step (b), said step of promoting the formation of dislocations within said resultant coating comprises regulating the temperature at which said first and second compounds are epitaxially grown.